Method and means for transmission and registration of signals



E. ZOLLER ET AL Nov. 3, 1936.

METHOD AND MEANS FOR TRANSMISSION AND REGISTRATION OF SIGNALS Filed April 8, 1 955 2 Sheets-Sheet 1 19 j b 20 Q Nov. 3, 1936- E. ZOLLER ETAL METHOD AND MEANS FOR TRANSMISSION AND REGISTRATION OF SIGNALS Filed April 8, 1933 2 SheetsSheet 2 a "Ale/"A5014? gomZol/er Patented Nov. 3, 1936 UNITED STATES PATENT OFFICE Egon Zoller and Josef Villiger, Zurich, Switzerland Application April 8, 1933, SerialNo. 665,164 In Germany March 24, 1932 17 Claims.

This invention relates to a method and means for the transmission and automatic registration of signals in automatic telephone installations, the number disc or a similar signal giving device being used to give the said signal.

In particular the present invention renders it possible to establish and maintain connection or communication between the calling and the called subscribers, even when the called subscriber does not answer and the calling currents cease to flow. At the same time the signals are so transmitted from the calling subscriber to the called subscriber by the method and the means employed in this invention that even when connection is made over long distances they are amplified by the amplifying exchanges situated between the central exchanges and so reach the called subscriber.

The means employed for carrying out the present invention may be applied Without any modification of existing apparatus by merely connecting up an additional appliance (in the shape of a receiver) at any desired subscriber, who is connected to an automatic telephone installation, and by connecting said receiver up in such a way that the mains remain free from extraneous currents completely.

According to this invention signals sent out by a calling station are superimposed upon a current in a circuit which maintains the recording apparatus at the called station in communication with the calling station. Preferably a carrier wave, which may be of speech frequency, produced at the calling station, is used for the transmission of signals sent out by the calling station and recorded at the called station.

In a preferred arrangement for carrying out the method according to this invention, the apparatus for producing the frequency, such as a buzzer or tube generator for example, lies in parallel with the impulse contact in such a way that when the impulse contact is operated, impulse current shocks and the carrier waves are produced at the same time, which can be sent over the subscribers line wire.

In a preferred constructional form of the arrangement according to this invention a step by step switch is first controlled for a series of steps by the calling current impulses over a relay, which then waits for a series of calling current impulses (the calling period) while a further number of steps prepares a Working circuit (preferably supplied independently of the mains) for the reception of the signals (preparation period) and finally, during the last step or steps, switches in a controlling circuit (preferably controlled by means of electrode tubes from the incoming signals) for the working circuit (the working period).

The invention will be best understood on referring to the drawings afiixed to our specification and forming part thereof, which illustrates an apparatus according to our invention.

Fig. 1 shows the connection between the two subscribers A and B when they are put through to each other.

Fig. 2 shows diagrammatically the system of connections at the subscribers apparatus on the calling side.

Fig. 3 shows the arrangement of a buzzer as the generator for the carrier wave of speech frequency.

Fig. 4 showsdiagrammatically the system of connections at the subscribers apparatus on the called side with switching in and amplifying circuits for the reception of the signals transmitted.

Fig. 5 shows the working circuit and also the recording device on the called side.

Figs. 6 and '7 show the switching stages and the arrangement ofcontacts for the step by step switch.

Firstly, both subscribers A and B are provided with the usual instruments. 5 is the ringing mechanism, 6 is the condenser, l is the fork of the receiver, 8 is the corresponding contact point, 9 is the microphone, l0 an inductive coupling, H the receiver, I2 the impulse contact operated by the number disc, [3 the short-circuiting contact likewise operated by the number disc. If the receiver be taken off its hook, a continuous current will flow in the usual way from the central station C1 over the conductor I, the contact points 1, 8, the inductive coupling in, the microphone 9, the impulse contact I2, and the conductor 2 back to the central station C1. This current serves inthe usual Way to operate the relay M of the'selecting devices at the central station 01. After a number has been selected and put through to the central station 02 an alternating current flows from this latter to the called subscriber B over the conductor 3, the calling relay E (see Fig. 4) the condenser 6, the ringing mechanism 5, the impulse contact [2 and back through the conductor 4. If the receiver be lifted off its hook on the called side, the speech connection is established in the usual Way. Now in order to be able to send signals from the calling subscriber to the called subscriber, even when this latter is absent and does not take his receiver'oif its hook, we employ according to this invention a carrier wave (preferably of speech frequency) produced at the calling station. For this purpose in the example illustrated in the drawing a frequency generator D, (1, such for example as a thermionic tube generator, or a buzzer, is connected up in parallel with the impulse contact l2 (see Fig. 2) across the pawl l5. At the called subscribers end l3 (see Fig. 4) there is a calling relay E connected up in series with the bell 5 and the condenser 6 and which first, under the action of the calling current impulses controls'by means ofits armature contact e a switching-in relay F lying between the subscribers conductors 3, 4 on the receiving side. On the called side there is also the line relay G, which forms a reserve load branch for the microphone and telephone and is fed by the supply current from the mains. The

inductive coil l6, which is likewise excited fro1n the main circuit, controls by means of the grid the thermionic tube l8, which in its turn controls the receiving relay H, which operates the writing apparatus 22 (see Fig. 5) by means of its armature contact h.

In the working circuit I9, 20, source of current 30 (see Fig. 5) is also placed the switching off relay J, the winding K of a time switch, e. g. a thermorelay, the step by step switch M and also a controlling relay P. To the working circuit are also connected the armature of the feed motor 2| of the writing apparatus 22 and also this latter itself.

The apparatus works as follows:-

When a subscriber A calls up a subscriber B the calling relay (preferably placed in the ringing current branch) at the called subscribers end will be energized in addition to the call bell (circuit: line wire 3, calling relay E, condenser 6, call bell 5, impulse contact l2, line wire 4) and controls first under the action of the calling current impulses by means of its armature contact e the switching-on relay F lying between the subscribers conductors 3, 4 of the called station. The switching-on relay F serves in the example illustrated to switch a working circuit I 9, 30, 20 supplied independently of the subscribers mains on to a controlling relay P, which serves to control a step by step switch M which is provided with armature contacts and fixed contacts and is likewise connected up to the working circuit. The switching-on relay has a high ohmic winding, so that the drop in the voltage is sufliciently great so as not to switch oiT the calling current at the central station and therefore the intermittent calling currents continue to be given by the central station. The relay F closes its contact I and is energized through its contact f1, and the controlling contact m1 of the step by step switch.

The step by step switch is provided with seven controlling contacts m1 to m: and two armature contacts ma, me.

The development of the several controlling stages 0-|9 of the step by step switch is shown in Fig. 6, while Fig. 7 shows the step by step switch with its switch magnet M, the escapement wheel 42, the controlling discs 26, 21, 28 and the contacts m1m9. The switching on relay F is connected by its contact to the working circuit, so that the controlling relay P of the step by step switch is energized from the source of current 30 over the conductor IS, the open circuit contact me of the step by step switch, also the controlling contact ms; of the step by step switch, the con tact f2, the conductor 20 from the source of current 30. The make and break relay P closes its contact 79, so that the step by step switch is energized (circuit: 30, I9, M, p, 11251, f2, 20). The step by step switch attracts its armature and interrupts, by opening the contact me, the make and break relay P, which now drops off and by opening the contact interrupts the step by step switch M again. By the dropping off of its armature the step by step switch M takes the first step from the position 0 to the position I (see Fig. 6). In this position the roller contacts 1721, mm will be opened while on the other hand the roller contacts m4, maII will be closed. By closing the contact m the step by step switch consequently after its first step switches on the source of current 30 to the working circuit and keeps it switched on until on the last step of the step by step switch, I9 to 0, the contact m4 is again opened and the source of current is consequently switched ofi from the working circuit. During the same time the contact bridge m5 is brought from position I into position II.

By this passage of the contact from 12251 to m5II the controlling relay P is denuded of current and a circuit 30, 20, 1124, men, gs, is, K, I9 for the thermorelay K is closed. If the thermorelay K remains switched on for a certain previously determined time, it connects the switching off relay J to the voltage of the working circuit by means of its armature contact, so that the whole arrangement is switched off in the manner to be hereinafter described.

When the step by step switch passes over from the position 0 to the position I the contact bridge m1 (see Fig. 4) is broken. This renders the switching on relay F devoid of current and opens its contacts f1 and f2. By the next calling current impulse which takes place at the called subscribers end, the calling relay E is again energized and closes its contact e. This connects the switching off relay F to the line again and the relay receives a current impulse which reverses the armature contact )3 of the switching on relay (see Fig. 5). This switches off the thermorelay K while on the other hand the step by step switch M is connected up over f2, 93, m5II, m; to the source of current 39 of the working circuit. When the current impulse has ceased there is no current passing in the relay E, the contact e drops oiT and the current ceases also to pass in the switching on relay F, so that its contact f3 again becomes reversed from M to K. By the switching off of the current from the step by step switch magnet a further step in the switching will be executed. The cycle of operations is repeated at every calling current impulse, so that after the working circuit has been switched on by the first step of the step by step switch, the switching on relay F by means of its contact 1%, at every predetermined number of calling current impulses, moves the step by step switch an idle step further in each case and so for a series of steps of the step by step switch waits for a predetermined number of calling current impulses.

This goes on until the step by step switch arrives in the position 5 shown in Fig. 6.

If, however, the called subscriber lifts his receiver all its hook during this period (the calling period) the calling current is switched off at the central station in the usual way and the speaking lines switched into circuit so that now the thermorelay K remains switched on over an open circuit contact f3 of the switching on relay F, and also 93, m51I, until its contact K connects up the switching off relay J to the voltage 30 of the working circuit across ml. The switching ofi" relay J closes its contact is, so that now the controlling relay P of the step by step switch is switched in to circuit and consequently the step by step switch itself across its working contact. As soon as the step by step switch is switched on its open circuit contact m9 opens, so that current again ceases to pass in the controlling relay, its working contact p opens and therefore cuts oil the current from the step by step switch.

This causes the step by step switch to move another step but it also and at the same time connects up its controlling relay P to the voltage across its open circuit contact m9, so that finally by an alternating cycle of movements the step by step switch will be brought back idly through all the steps into the original position by means of the contacts p and me.

The arrangement may also be so constructed that the step by step switch is brought back directly into the original position by the thermorelay which may also be replaced by any other desired kind of time switch. If on the contrary the receiver be not taken off its hook and the step by step switch moves through the'transition from position 4 to position 5, the apparatus now enters the preparatory period, in which the working circuit is prepared for the reception of the signals. In position 5, as can be seen from the diagram in Fig. 6, the contact bridges m2, me of the step by stepswitch are closed, until, in the example illustrated, the step by step switch arrives in position l9. By the closing of the contact me the controlling relay P of the step by step switch will be connected up to the voltage 30 of the working circuit across the open circuit contact m9, so that now excitation takes place across the contact p of the magnet of the step by step switch M and its open circuit contact me is then open so that the current ceases to pass in P whereupon its working contact p opens and consequently switches the magnet of the step by step switch out of circuit. The step by step switch makes a step and at the same time it'closes its open circuit contact his so that the controlling relay P is again supplied with current and the cycle commences over again, so that the step by step switch is taken in succession through the steps or stages of this period until stage I8 is reached. By closing the contact bridge mg, every time the magnet of the step by step switch M is energized the armature contact m8 of the step by step switch will be closed and opens again when the magnet of the step by step switch is deenergized. When the contact ms is closed for the first time the subscribers line 3, 4 will be closed across the low ohmic winding I of the line relay G, so that the calling current will be switched off at the central station in the usual way and the speech conductors switched into circuit. The energized line relay G closes its working contact 91, so that the high ohmic winding II of the line relay G will be switched into circuit and remains switched into circuit across the contact g1. The winding II of the line relay (3- is so dimensioned that the relays 29 (see Fig. 1) hold with suificient security at the central station (circuit: 3, i1, windings I and II of the relay G, contact 91, impulse contact I2, line 4) The line relay G serves therefore as a substitution load branch for the microphone and inductive coupling supplied with current by the supply current of the mains, which is switched into circuit at the beginning of the preparation period.

On moving the step by step switch still further forward the high ohmic winding of the relay G II will be periodically short-circuited and switched into circuit by the alternate closing and opening of the step by step switch contact me, so that current impulses are produced at every step, and pass to the calling subscriber over the mains. This winding may therefore act as a giver of impulses lying in the substitution circuit and con trolled by the step by step switch and sending impulses to the calling station thereby indicating that the receiving apparatus has been prepared for reception and is ready. I

The line relay has in the working circuit a working contact 92 which, as soon as it is switched into circuit connects the feed motor 2| of the writing apparatus 22 to the voltage 30 of the working circuit, so that now the paper band or strip provided for the reception of the signals transmitted is moved past in front of the writing apparatus 44. At the same time the contacts g4, g5, gs of the line relay are switched into thethermionic tube circuit l8, so that the voltage 3| is connected up to the anode circuit, a heating voltage 32 to the incandescent cathode and finally a bias 33 to the grid. The grid bias is so dimensioned that at first no anode current flows, as long as no signals or frequency impulses pass over the subscribers line to the tube circuit. As soon as the step by step switch has reached position IS, the preparation period is over and the working period, that is to say the period in which the signal is transmitted, begins.

In position l9 the contact m6, m2 of the step by step switch will be cut outof circuit (see Fig. 6) so that the step by step switch at first remains in its position. In order to prevent'its'being moved further forward by the thermorelay an open circuit contact as of the line relay G is placed in the circuit of the thermorelay K and opens as soon as the linerelay is energized. The thermorelay or any other kind of time relay placed in. this circuit remains unenergized so that the further movement or advance of the step by step switch is prevented by this means also. In position I9 the contact bridges m3, 1117 are closed. By means of the contact bridge mg the primary winding I of the inductive coupling l6 e. g. a

ing subscriber energizing the grid of the electrode tube.

As soon as the calling subscriber hears the impulses produced by the alternate opening and closing of the winding G II which he will by hearing a snapping sound, the calling subscriber puts by means of the pawl [5 the frequency producer of the carrier wave of speech frequency, e. g. a buzzer D (see Figs. 2 and 3) in parallel with the impulse contact l2. scriber gives by means of his number disc or similar signal giving device coupled to the number disc, signals, a line current will flow during the opening time of the impulse contact through the frequency producer or generator, the buzzer D, and energizes (circuit: line I, short circuit contact l3, buzzer D, contact l5, line 2). The winding of the buzzer is so dimensioned that the relays l4 at the central station C I (see Fig. 1) still hold with sufficient security during the opening If now the calling subtime of the impulse contact I 2. The armature 23 of the buzzer D is rigidly attached at one end to the spring 24 the other end of which is attached to the casing 25. The contact (I is operated by the armature 23 and is connected up in parallel with the coil D. During the opening time of the impulse contact 12 the buzzer consequently is caused to vibrate with a frequency which corresponds to the frequency of speech, and therefore produces carrier waves of speech frequency over the line I, 2 said waves passing over the central stations and the amplifying stations to the subscriber B, are then amplified by the central stations in the same way as the speech currents are amplified and behave in the mains in the same way as the speech currents.

At the called station the impulses received pass over the conductors 3, 4 the contacts 91, ms the condenser IT, to the primary winding I of the repeater and from the secondary winding thereof at a tension corresponding to the ratio of transmission into the controlling circuit, in which they control the grid of the electrode tube. This causes the receiving relay H in the anode circuit to respond and operate its contact h in the working circuit I9, 20. By this means the writing magnet 22 will be operated in accordance with the number of the impulses given by the calling subscriber by means of his number disc for example.

When the giving of the signals is over or the calling subscriber hangs up his receiver for any reason, a closing impulse is produced in the line 3, 4. The line relay G drops off, opens its holding contact 91 and also the contacts g4, g5 and gs. It also closes its contact ya, so that now the controlling relay P is energized over 19, P, m9, mi, 93, msII, m4 and the conductor 20 and energizes by means of its contact 10 the step by step switch. This latter opens its contact me and the current is cut off therefrom the now deenergized relay P opening its contact p. By this means the step by step switch makes its last step into' the original position 0, thereby opening the contacts m3, m7 also the contacts 1m, 1m and brings the contact bridge 1215 into position I. By this means all circuits, controlling circuits, working circuits are switched oil and at the same time the connections of the installation prepared for a fresh recording.

Instead of moving the step by step switch forward from the position l9 into the zero position the apparatus may also be so constructed that the step by step switch is returned to the original position over the previous steps.

It has been described above how the step by step switch is brought idly through all the steps or stages and back into the original position under the action of the time switch K and the switching off relay J when the receiver is taken off the hook at the receiving end during the calling period and the recording apparatus thus switched off. The apparatus works in a similar manner if the calling subscriber hangs up the receiver or it be taken off the hook at the station called both during the calling period and also during the period of preparation.

In all these cases (during the positions I to H] of the switch in the example shown, l9 also) the time switch or the thermorelay will be energized from the source of current 30 and as a matter of fact over m4, msII, g3, f3. If none of the relays F, G be energized the circuit of the thermorelay remains closed until after a certain time the contact It is iwitched into circuit and the switching-off relay J thus switched on, the working contact 12 of which operates the step by step switch M by means of its controlling relay P, which in the manner above described brings by alternate switching cycles and by means of the contacts 10 and ms the step by step switch idly through all the steps or stages or returns it to the original position until finally in the original position the contact m4 opens m5 is brought into position I and therefore the thermorelay and the switching-off relay switched out of circuit also.

The switching-off relay has in the substitution circuit branch formed by the line relay G an open circuit contact '1, which when the switching-off relay brings the step by step switch into the original position, opens, so that the circuits which are dependent on the substitution circuit branch or the line relay G are uncontrolled and the subscribers loops remain free.

We claim as our invention:

1. In an automatic telephone installation having conductor lines, a calling station, a called station, a source of direct voltage within the exchange of the calling station for interconnecting said calling station to the lines, a signal recording apparatus at the called station, said calling station further comprising an impulse transmitter having an impulse contact and a source of alternating voltage, means for connecting said source of alternating voltage in parallel to the impulse contact of said impulse transmitter and for producing alternating current impulses in the exchange direct current, said alternating current impulses serving to operate said recording apparatus at the called station.

2. An automatic telephone installation as specified in claim 1, comprising a buzzer in the calling station, said buzzer consisting of a magnet coil and an armature, both being connected in parallel to the impulse contact of the transmitter, said buzzer constituting a generator of speech frequency, whereby upon opening of the impulse contact the exchange current actuates the buzzer, said magnet coil being dimensioned so that the relays of the exchange will be held.

3. In an automatic telephone installation including an exchange circuit, a calling station, a called station, a signal recording apparatus at the called station, an impulse transmitter at the calling station for producing current impulses in the exchange circuit to operate said signal recording apparatus at the calling station, an automatic step by step switch and a calling circuit at the called station, and controlling circuits for said signal recording apparatus to record the signals, said step by step switch being provided with controlling means adapted to step it through all steps and to its original position from any position in response to the action of hanging up the receiver at the calling station or in response to the action of removing the receiver from its hook at the called station, said means being controlled independently from any signals or impulses of the lines.

4. In an automatic telephone installation including an exchange circuit, a calling station, a called station, a signal recording apparatus at the called station, an impulse transmitter at the calling station for producing current impulses in the exchange circuit to operate said signal recording apparatus at the called station, said called station further comprising an automatic step by step switch and a calling circuit, a calling relay for interconnecting said calling circuit during a first series of steps to said step by step switch; said signal recording apparatus comprising a working circuit to record the signals in said signal. recording apparatus, a separate source of voltage for feeding said working circuit, a preparing circuit for said working circuit, and a control circuit for controlling said working circuit; means associated with said step by step switch for disconnecting said calling circuit and said calling relay at the end of said first series of steps; a controlling relay associated with a steering magnet of said step by step switch, thev controlling relay and steering magnet having contactmeans within their mutual circuits, for efiecting automatic advance of the step by step switch through a second series of steps on to the recording step; the step by step switch including contact means associated with said preparing circuit for connecting said preparing circuit to the lines during said second series of steps; and said step by step switch being further provided with contact means associated with the preparing circuit for connecting said control circuit to its source ofvoltage and energizing means during said recording step of said step by step switch.

5. An automatic telephone installation as specified in claim 4, said calling relay having allotted to it a high ohmic switching-on relay, means for connecting said switching-on relay between the lines of the called station, and circuit meansassociated with said calling relay and said switching-on relay and for controlling said switching-on relay from said calling relay under the action of the calling current impulses, said switching-on relay serving to switch on the signal recording apparatus upon failure of the called station to answer.

6. An automatic telephone installation as specified in claim 4, said calling relay having allotted to it a high ohmic switching-on relay, means for connecting said switching-on relay between the lines of the called station, circuits associated with said calling relay and said switching-on relay and for controlling said switching-on relay from said calling relay under the action of the calling current impulses, said switching-on relay serving to switch on said controlling relay for advancing said step by step switch a first step out of its rest or zero position upon failure of the called station to answer.

'7. An automatic telephone installation as specified in claim 4, said step by step switch being provided with armature contacts and bridge contacts, and circuit means for switch connection of said source of voltage to said working circuit by means of a first step bridge contact of said step by step switch, one of said armature contacts serving to control said controlling relay during said first series of steps of said step by step switch.

8. An automatic telephone installation as specified in claim 4, said calling relay having allotted to it a high ohmic switchingon relay, means for connecting said switching-on relay between the lines of the called station, and circuits associated with said calling relay and said switching-on relay and for controlling said switching-on relay from said calling relay under the action of the calling current impulses, said switching-on relay serving to switch on the signal recording apparatus upon failure of the called station to answer, said switching-on relay further comprising a contact allotted to said steering magnet of said step by step switch and adapted to advance the step by step switch at each of a predetermined number of calling im pulses without further operation occurring until a predetermined number of calling impulses have been received.

9. In an automatic telephone installation including an exchange circuit, a calling station, a called station, a signal recording apparatus at the called station, an impulse transmitter at the calling station for producing current impulses in the exchange circuit to operate said signal recording apparatus at the called station; said called station further comprising an automatic step by step switch and a calling circuit; a calling relay for interconnecting said calling circuit during a first series of steps to said step by step switch; said signal recording apparatus comprising a working circuit to record the signals in said signal recording apparatus, a separate source of voltage for feeding said working circuit, a preparing circuit for said working circuit, and a control circuit for controlling said working circuit; means associated with said step by step switch for disconnecting said calling circuit and said calling relay at the end of said first series of steps; a controlling relay associated with a steering magnet of said step by step switch, the controlling relay and steering magnet having contact means within their mutual circuits, for effecting automatic advance of the step by step switch through a second series of stepson to the recording step; said step by step means having contact means associated with said preparing circuit for connecting said preparing circuit to the lines during said second series of steps; said step by step switch being further provided with contact means associated with said preparing circuit for connecting said control circuit to its source. of voltage and energizing means during said recording step of said step by step switch; said called station further comprising a substitution load branch, said substitution load branch being an electrical equivalent to microphone, inductive coupling and receiver of the called station; switching means associated with said step by step switch for bridging said substitution load branch across the called partys lines, circuit means for feeding said substitution load branch from the called station, and switching means for connecting said substitution load branch to said preparing circuit.

10. An automatic telephone installation, as specified in claim 4, the called station further comprising a substitution load branch for the microphone and for the inductive coupling of the called station, circuit means for feeding said substitution load branch from the called station, and switching means for connecting said substitution load branch to said preparing circuit, said substitution load branch including an impulse generator, and means for controlling said impulse generator by said step by step switch, said impulse generator serving to send impulses to the calling station over the lines and. to indicate that the recording apparatus is ready to record signals.

11. An automatic telephone installation, as specified in claim 4, the called station further comprising a substitution load branch for the microphone and for the inductive coupling of the called station, circuit means for feeding said substitution load branch from the called station, switching means for connecting said substitution load branch to said preparing circuit, said substitution load branch including a relay with a low ohmic winding and a high ohmic winding, and means associated with said step by step switch for periodically short circuiting said high ohmic winding and for sending impulses to the calling station over the lines for indicating that the recording apparatus is ready to record signals.

12. An automatic telephone installation, as specified in claim 9, said substitution load branch further comprising a relay for controlling the connection of said separate source of current for the working circuit to the recorder of said recording apparatus.

13. An automatic telephone installation, as specified in claim 4, the called station comprising an inductive coupling consisting of a primary winding and a secondary winding, said step by step switch comprising switching means for connecting said primary winding to the called station, at the working step of said step by step switch, the called station further comprising a thermionic tube consisting of an anode, a cathode, and a grid, said grid being controlled by the secondary winding of said inductive coupling, and switching means for including said anode and said cathode in said control circuit.

14. An automatic telephone installation, as specified in claim 4, the called station comprising an inductive coupling consisting of a primary winding and a secondary winding, said step by step switch comprising switching means for connecting said primary winding to the called station at the working step of the step by step switch, the called station further comprising a thermionic tube consisting of an anode, a cathode, and a grid, said grid being controlled by the secondary 'winding of said inductive coupling, and switching means for inserting said anode and said cathode into said control circuit, said control circuit further comprising a source of voltage with a contact, said contact being associated with said recording apparatus.

15. An automatic telephone installation, as specified in claim 9; said substitution load branch further comprising a relay for controlling the connection of said separate source of current for the working circuit to the recorder of said recording apparatus; said relay comprising a back contact, said back contact being associated with said controlling relay for operating the same and for actuating said step by step switch to step it out of the recording step to its original rest position thereby disconnecting the recording apparatus as soon as transmission is completed and the receiver has been hung up at the calling station and the substitution load branch has the current cut ofi from it.

16. An automatic telephone installation, as specified in claim 4, said working circuit comprising a time switch, means associated to said time switch for causing automatic stepping of said step by step switch forth through all steps and to its original position or rest position, from any position, and further means associated to said time switch for switching off the recording apparatus during the calling period or during the preparation period, in response to the action of hanging up the receiver at the calling station or in response to the action of removing the receiver from its hook at the called station.

17. An automatic telephone installation as specified in claim 3, the called station further comprising a substitution load branch; said substitution load branch being an electric equivalent to microphone, inductive coupling and receiver of the called station; circuit and switching means for announcing to the calling station of the readiness of the recording apparatus for signal record ing, circuit and switching means for bridging said substitution load branch across the lines, means for controlling said working circuit from said substitution load branch, recording means for being actuated from the signals arriving, said working circuit comprising a time switch and a out 01f relay associated with said time switch, and relay and circuit means for stepping said step by step switch back to its original position as soon as transmission is ended or no longer wanted, switching means being associated with said cut off relay for opening the circuit of the substitution load branch during the time said step by step switch returns to its original or rest position and for holding uncontrolled the circuits dependent upon the substitution load branch and for holding the called station open.

EGON ZOLLER. JOSEF VILLIGER. 

